Mohid Ocean Downscalling

Download

MyOcean

To download my ocean solution go to http://www.myocean.eu/. and click in ACCES THE CATALOGUE. In block 1 choose "Global Ocean", in 2 the parameters and in 3 choose forecast products. After fill all the blocks click search and in the next web page choose DATA ACCES and then GO. Prescribe the user name and password and then choose the dates and area of interest.

NOOA : GFS, RTOFS

Conversion

grib-netcdf-hdf5

Bathymetry transition

Running tool SmoothBathymNesting.exe

Example of the input file SmoothBathymNesting.dat

! File bathymetry of the external 3D solution
FATHER_BATIM                : 
!Bathymetry File of MOHID solution
SON_BATIM                   : 

!New Bathymetry File 
NEW_SON_BATIM               : 
<begin_coef>
NAME                        : generic property !Name of generic property
INITIALIZATION_METHOD       : sponge           !Type of initialization used
DEFAULTVALUE                : 1                !0-external 3D solution, 1-MOHID solution
SPONGE_OUT                  : 0
SPONGE_CELLS                : 10               !sponge cells number
SPONGE_EVOLUTION            : 2                !1-exponential, 2-linear
<end_coef>

Interpolation

z-level to MOHID geo

bilinear vs triangulation

linear horizontally and vertically

Boundary conditions

Open boundary

high frequency vs low frequency = mohid 2D + 3D external solution

radiation + flow relaxation scheme

Surface

To impose surface boundary conditions (e.g., wind stress, solar radiation, temperature, pressure etc.) an example of the file is provided below.

<begin_rugosity> INITIALIZATION_METHOD  : CONSTANT DEFAULTVALUE  : 0.0025 <end_rugosity>

Compute sensible heat, latent heat based in the water/air temperature, wind, relative humidity

Iinital condition and Spin up

For the spin-up procedure, a methodology based on a slow connection of the forcing terms (baroclinic force, windstress) is used. This methodology consists of defining an initial condition where the initial fields of salinity and temperature are interpolated from the external 3D solution (MyOcean or RTOFS), a null velocity field is assumed, and a SSH field with null gradient is also considered. A coefficient that varies linearly between 0 and 1 along the “connection” period of 5 days is multiplied by the baroclinic force and wind stress. Because the forces are slowly connected, the velocity reference solution of the OBC also needs to be slowly connected. The nudging term in the momentum equation is multiplied by a coefficient C given by:

$C=(Elapsed Time/Connection Period)^4; Elapsed Time<Connection Period$

$C=1 ; Elapsed Time>=Connection Period$

In this way, the velocity field near the boundary also converges slowly to the reference solution. To minimize the perturbations suffered by the initial condition of salinity and temperature along the spin-up period, a relaxation period variable in time was also assumed for these properties. The idea is to assume a relaxation period that increases with time; this way, in the beginning of the run the temperature and salinity fields have a stronger nudging when the external and internal activity is more intense due to the spin-up process. In the end of the spin-up period, the nudging in the model interior (out of the FRS area) is null. For the forces, a connection coefficient was assumed with a linear evolution over 5 days. For the reference solution a quadratic evolution was imposed. For the slow connection of the forcing mechanisms, the methodology followed by Mellor (2004) for the baroclinic force was assumed. This evolution allows, in the first instants, a strong nudging across the entire domain. With time, the model tends to be free except in the flow relaxation scheme area.

slow connection of terms: wind, tide, atmospheric pressure, baroclinc force

initial condition : salinity and temperature from external solutions, null sea level gradient and null velocities

initial strong relaxation of temperature and salinity in all domain